How does water suspended in more water not boil? ( I think it can be called a double boiler )

Question

I found this TikTok but I didn’t quite grasp it. https://vm.tiktok.com/ZMYFDecSL/

In: 3

Answer 1

At normal room pressure water boils at 100°C. The steam that is generated is also at 100°C. It can’t get hotter than that unless you seal it and allow the pressure to increase (which is how pressure cookers work).

In a heated vessel where you are heating the base, the top surface is cooling, and the liquid between the top and the bottom is going to sit somewhere between the cooler top surface temperature and the hot base temperature.

In a double boiler (or bain marie) situation the bottom of the inner container is only ever getting heated by the steam (or water) from he boiling lower container, so it only ever gets to 100°C, so it’s impossible for the liquid inside the upper container to get hotter than that.